Python Project: Temperature Converter

What you are building

You write small functions that convert among Celsius, Fahrenheit, and Kelvin. Each formula lives in one place. A table of sample values proves the functions agree with the usual checkpoints: water freezes, room temperature, body temperature, and water boils.

Run everything at /try. That editor executes Python. It is not an HTML preview and not a C or C++ compile step. Values are listed in the script, so you never type into input().

Skills used

• One function per conversion
• Arithmetic with float values
• round when you want a short printed figure
• Calling one converter from another (Fahrenheit through Celsius into Kelvin)
• Formatted columns so the table is readable

Put each formula in a function

Celsius to Fahrenheit is multiply by 9 / 5, then add 32. The inverse subtracts 32, then multiplies by 5 / 9. Kelvin is Celsius plus 273.15. Name those steps. Do not copy the numbers into every print line.

def c_to_f(c):
    return c * 9 / 5 + 32

def f_to_c(f):
    return (f - 32) * 5 / 9

def c_to_k(c):
    return c + 273.15

print(c_to_f(0))
print(f_to_c(32))
print(c_to_k(0))

Zero Celsius should print 32.0, 32 Fahrenheit should print 0.0, and zero Celsius should print 273.15 Kelvin. If any of those fail, fix the function before you build the table.

Reuse Celsius as the hub

You do not need six independent formulas. Convert Fahrenheit to Kelvin by going through Celsius. Convert Kelvin to Fahrenheit the same way. Then a bug in c_to_f is still only in one function.

def c_to_f(c):
    return c * 9 / 5 + 32

def f_to_c(f):
    return (f - 32) * 5 / 9

def c_to_k(c):
    return c + 273.15

def k_to_c(k):
    return k - 273.15

def f_to_k(f):
    return c_to_k(f_to_c(f))

def k_to_f(k):
    return c_to_f(k_to_c(k))

print(round(f_to_k(32), 2))
print(round(k_to_f(273.15), 2))

Complete program

Four Celsius samples fill a printed table of F and K. A second block converts a few Fahrenheit values back, so you see both directions. Copy the whole file into /try.

def c_to_f(c):
    return c * 9 / 5 + 32

def f_to_c(f):
    return (f - 32) * 5 / 9

def c_to_k(c):
    return c + 273.15

def k_to_c(k):
    return k - 273.15

def f_to_k(f):
    return c_to_k(f_to_c(f))

def k_to_f(k):
    return c_to_f(k_to_c(k))

samples_c = [0, 21, 37, 100]

print("Temperature converter")
print()
print(f"{'C':>8} {'F':>8} {'K':>8}")
for c in samples_c:
    print(f"{c:8.1f} {c_to_f(c):8.1f} {c_to_k(c):8.2f}")

print()
print("Checks from Fahrenheit")
for f in [32, 70, 212]:
    c = f_to_c(f)
    k = f_to_k(f)
    print(f, "F ->", round(c, 2), "C,", round(k, 2), "K")

Common mistakes

• Writing c * (9 / 5 + 32) folds 32 into the scale factor. Usec * 9 / 5 + 32. The inverse needs parentheses: (f - 32) * 5 / 9.
• Using 273 instead of 273.15. The table will then miss every Kelvin value by 0.15.
• Integer division in another language. In Python 3, 9 / 5 is 1.8. You do not need9.0, but you must not use //.
• Rounding inside the function. Keep full precision in the return value. Round only when you print.
• Mixing scales in one variable name. Call the Celsius value c, not temp, once Fahrenheit is in the same file.

How to extend / Practice tasks

Keep the functions. Change the samples or the rounding.

1. Add -40 to samples_c. Celsius and Fahrenheit meet at -40. Print that row and confirm both columns show -40.0.
2. Write format_row(c) that returns one formatted string, then print with a loop that only calls that helper.
3. Convert 0 Kelvin to Celsius and Fahrenheit and print a warning if Celsius is below -273.15, the absolute zero floor this project does not otherwise enforce.